Ovarian cancer represents a heterogeneous group of diseases that affect women on a global basis. There are several forms of ovarian cancer which include epithelial cancer, germ-line cancer of the ovaries and ovarian stromal cancer. Epithelial ovarian cancer represents the most common form of the disease. Approximately 5-10% of epithelial ovarian cancer represents a hereditary form of the disease and three common patterns are recognized: ovarian cancer alone; ovarian and breast cancer linked to BRAC1 and BRCA2 genetic linkage on chromosomes 17q21 and 13q12 respectively; and ovarian and colon cancer. The most important risk factor for ovarian cancer is a first degree relative with the disease (e.g., a mother, sister or daughter with ovarian cancer). See, for example, Patridge et al. (1999) CA-A Cancer Journal for Clinicians 49:297-320. In 2005, there were an estimated 22,000 new cases of ovarian cancer diagnoses and 16,000 deaths from ovarian cancer. See generally American Cancer Society website at www.cancer.org; National Cancer Institute website at www.cancer.gov. Ovarian cancer is a disease that primarily affects post-menopausal women with the median age for diagnosis at 63 years of age. However, the disease can affect women at all age groups. National Cancer Institute Surveillance, Epidemiology, and End Results (SEER) Program at www.seer.cancer.gov.
The classification of ovarian cancer stage is based upon the extent of localization versus spread of the disease beyond the ovaries. Stage 1 ovarian cancer is confined to one or both of the ovaries. Stage 2 disease involves a tumor in one or both ovaries with pelvic extension. In Stage 3 ovarian cancer, a tumor is present in or both ovaries with microscopically confirmed peritoneal metastasis outside the pelvis and/or regional lymph node metastasis. Stage 4 ovarian cancer is characterized by distant metastasis beyond the peritoneal cavity. Ovarian cancer is generally diagnosed in an advance stage of the disease due to the lack of specific clinical symptoms that would indicate the presence of small tumors. For women under the age of 50, less than 40% of ovarian cancers are detected when tumors are localized to one or both ovaries and when disease prognosis is best. For women over the age of 50, that number drops to less than 15%. Approximately 68% of women of all age groups afflicted with ovarian cancer are not diagnosed until distant metastasis is present. See generally National Cancer Institute Surveillance, Epidemiology, and End Results (SEER) Program at www.seer.cancer.gov.
Ovarian cancer spreads via local shedding from the ovarian epithelium into the peritoneal cavity followed by implantation on the peritoneum and local invasion of the bowel and bladder. The presence of lymph node involvement in ovarian cancer is evident in all stages of diagnosed ovarian cancer. The percentage of positive lymph nodes increases significantly with progression of the disease (i.e., Stage 1, 24%; Stage 2, 50%, Stage 3, 74%; Stage 4, 73%). Id.
The survival of patients with ovarian cancer is a function of the stage at which the disease is diagnosed, with the 5-year survival decreasing with advanced disease. More than 90% of women diagnosed with ovarian cancer in Stage 1 survive for at least 5 years following diagnosis. The 5-year survival rate drops to less than 30% when the disease is not diagnosed until Stage 4 (i.e., distant metastasis). Id.
Epithelial ovarian cancer is the most common form of the disease. There are four recognized major histological classes of epithelial ovarian cancer and include serous, endometrioid, clear cell, and mucinous subtypes. The pathogenesis of ovarian cancer is poorly understood but is believed to arise from ovarian surface epithelium. See Bell (2005) Mod. Pathol. 18 (Suppl 2):S19-32. Life factors that provide the greatest reduction in risk of ovarian cancer include multiparity, use of oral contraceptives, and breast feeding, all of which prevent ovulation. Because ovulation results in epithelial damage, followed by repair and possible inflammatory responses, repetition of this process throughout a woman's reproductive life without interruption appears to lead to cell damage and to increase the risk of ovarian cancer. See, for example, Ness et al. (1999) J. Natl. Cancer Inst. 91:1459-1467. However, there is no recognized, stepwise progression of ovarian cancer through defined precursor lesions, such as those recognized for both cervical carcinoma and colon cancer. Hence, considerable research has been directed at understanding the molecular basis for ovarian cancer and to understand the basic differences between the various histological subtypes of ovarian cancer. These studies have utilized gene expression analysis to provide this understanding and have identified a series of potential biomarkers for evaluation in diagnostic applications. See for example Ono et al. (2000) Cancer Res. 60:5007-11; Welsh et al. (2001) Proc. Natl. Acad. Sci. USA 98:1176-1181; Donninger et al. (2004) Oncogene 23:8065-8077; and Lee et al. (2004) Int. J. Oncol. 24(4):847-851.
Ovarian cancer is often detected with the presentation of overt clinical symptoms, most notably the presentation of abdominal pain, an adnexal mass, abdominal bloating, and urinary urgency. As such, the detection of ovarian cancer is often detected at an advanced stage, where the prognosis and clinical outcome is poor. Detection of ovarian cancer at an early stage (i.e., Stage 1) results in approximately 90% cure rate using standard surgery and chemotherapy; hence there is a clinical need to detect ovarian cancer at an early stage where treatment will be most effective. Unfortunately, current screening methods to detect early stage ovarian cancer are insufficient. The current practice for ovarian cancer screening employs the use of CA125 and transvaginal ultrasound (sonography). Rising serum levels of CA125 are associated with ovarian cancer and subsequent utilization of transvaginal ultrasound helps detect the presence of ovarian cancer. Confirmation of ovarian disease is based upon invasive procedures such as laparotomy. However, the use of CA125 is ineffective for general population screening due to issues of limited sensitivity, limited specificity, and a poor positive predictive value of <3%. Bast (2003) J Clin Oncol. 21(10 Suppl):200-205. As a result, there is no consensus on the recommendations for generally screening for ovarian cancer in the asymptomatic patient population. See National Cancer Institute Web Site at www.cancer.gov. For high risk patients, the generally accepted procedures for the detection of ovarian cancer include the use of pelvic examinations, the use of CA125 serum testing, and transvaginal ultrasound (sonography). Patridge et al. (1999) CA-A Cancer Journal for Clinicians 49:297-320.
CA125 is a well characterized tumor marker normally expressed on the surface of epithelial cells and is often detected in the serum of normal patients at 35 U/mL. Elevated serum levels of CA125 (>35 U/mL) are often detected in approximately 85% of ovarian cancer patients; the remaining 15% of ovarian cancer patients have normal serum levels of CA125. Furthermore, CA125 is elevated in only 50% of stage 1 ovarian cancer patients, thereby limiting its clinical utility in the early detection of ovarian cancer. However, elevated serum levels of CA125 are used for the monitoring of disease recurrence following therapeutic intervention and this represents the currently approved use for CA125 by the FDA. In addition, elevated serum levels of CA125 are predictive of future detectable ovarian cancer.
The low prevalence rates of ovarian cancer in the general population create significant challenges for the development of a screening test that would promote early detection of the disease. Screening methods for diseases with low prevalence rates such as ovarian cancer often result in a high ratio of false positives to true positives, which limits the clinical utility of such screening programs. Given the significant risks associated with surgical exploration for possible ovarian cancer, a clinically useful screening test should refer to surgery no more than 10 women for every woman who actually has ovarian cancer (i.e., a positive predictive value (PPV) of at least 10%). Skates et al. (2004) J. Clin. Oncol. 22:4059-4066. PPV is highly dependent upon the prevalence rates for a particular disease or condition and will shift dramatically as a result of differences in disease prevalence. Therefore, with low-prevalence diseases, such as ovarian cancer, screening diagnostic tests with a relatively low PPV still have significant clinical utility. Potential ovarian cancer screening programs must be adjusted for the low prevalence of ovarian cancer and assessed for biomarker performance and clinical need. See, for example, Skates et al. (2004) J. Clin. Oncol. 22:4059-4066; Bast et al. (2005) Int. J. Gynecol. Cancer 15:274-281; and Rosen et al. (2005) Gyn. Oncol. 99:267-277. Despite efforts to identify a biomarker or panel of biomarkers for the detection, particularly early detection, of ovarian cancer, no adequate screening or diagnostic test that satisfies clinical needs currently exists. Currently available methods, such as detection of CA125, exhibit unacceptably high false-positive rates.
The current recommendations from the National Cancer Institute state that “there is insufficient evidence to establish that screening for ovarian cancer with serum markers such as CA125, transvaginal ultrasound or pelvic examinations would result in a decrease in mortality from ovarian cancer” (NCI Summary of Evidence (Level 4, 5); dated February 2005). In light of the serious risk of false-positives with currently available screening techniques, the NCI has not supported institution of general screening procedures for ovarian cancer. As such, no standardized screening test exists for ovarian cancer.
The 5-year survival rate for ovarian cancer, for example epithelial ovarian cancer (EOC), depends greatly on the stage of the disease at the time of diagnosis; increased survival is associated with early detection (i.e., Stage 1 or 2). The vast majority of ovarian cancers, however, are not diagnosed until stage 3 or 4, when prognosis is poor. Therefore, there is a need to identify more ovarian cancers at an earlier stage. The characterization of biomarkers that permit earlier identification of ovarian cancers has the potential to improve the clinical outcome for many patients. One such candidate biomarker is human epididymis protein 4 (HE4). HE4 is a secreted and glycosylated protein that was first observed in human epididymis tissue and is overexpressed in certain cancers, including ovarian and breast cancers. Subsequent studies have shown that HE4 protein is also present in the female reproductive tract and other epithelial tissues. The HE4 gene resides on human chromosome 20q12-13.1, and the 20q12 chromosome region has been found to be frequently amplified in ovarian carcinomas. See, for example, Bouchard et al. (2006) at oncology.thelancet.com 7:167-174; Galagono et al. (2006) Mod. Patholo. 19:847-583; Drapin et al. (2005) Cancer Research 65(6): 2162-9; Lu et al. (2004) Clin. Cancer Res. 10:3291-3300; Hellström et al. (2003) Cancer Research 63: 3695-3700; and Bingle et al. (2002) Oncogene 21: 2768-2773, all of which are herein incorporated by reference in their entirety. Accordingly, overexpression of HE4 in ovarian cancer cells suggests that this protein could be used as a biomarker in methods for detecting ovarian cancer or for identifying patients having an increased likelihood of having ovarian cancer.
In light of the above, a need exists in the art for antibodies that are capable of detecting expression of biomarkers, such as HE4, the overexpression of which may be indicative of ovarian cancer or an increased likelihood of a patient having ovarian cancer. Such antibodies could be used in methods for diagnosing ovarian cancer or for identifying patients having an increased likelihood of having ovarian cancer.